Sudanese protesters have described how they were force-fed sewage water and shot with live ammunition by security forces during a crackdown in Khartoum last week in which more than 100 people died, according to opposition activists.

In footage posted online, one protesters can be seen describing how he was brutally beaten by security forces who also burned parts of his hair. He said soldiers had also forced him to drink sewage water even though he was fasting for Ramadan.

Another video shows a protester laying in a hospital bed claiming that security forces had killed 10 people in front of him.

"He was hit in the left arm above his crotch here and in his leg," a doctor who is caring for the protester says. "On the right foot, he's missing three toes."

Four protesters were reported dead in the latest violence on Sunday as opposition groups called for a show of mass civil disobedience against the military council currently governing the country.

"We, as the Sudanese people, we don't care if they kill us, we don't care if they imprison us, we don't care about whatever they have done," said one protestor from a hospital bed in Khartoum.

"The only thing that we want is for Sudan to be a civilian-run country, a country with foundations [and] a country that protects its people."

Three detained rebels released

Sudanese authorities said on Monday that they had released three prominent rebels who were detained during the crackdown, state television reported.

Yasir Arman, deputy chief of the Sudan People's Liberation Movement-North (SPLM-N), was released along with two other leading rebels from the group, Ismail Jalab and Mubarak Ardol, it said, but did not specify when.

Arman had arrived in Khartoum on 26 May to take part in talks with Sudan's ruling generals who took power after the ousting of president Omar al-Bashir in April, following months of mass protests against his authoritarian rule.

He was seized on 5 June, two days after men in military fatigues raided a weeks-long protest sit-in outside the army headquarters in the capital.

Jalab and Ardol were seized from their residences after meeting with visiting Ethiopian Prime Minister Abiy Ahmed in Khartoum on Friday for talks aimed at reviving negotiations between the generals and protest leaders.

Alliance conditions

The SPLM-N's armed wing had battled Bashir's forces in the Blue Nile and South Kordofan states since 2011.